This invention relates to polymerizable dental resins for dental composite materials and the method of manufacture of such resins for restorative dentistry, and more particularly to dental composite materials that are useful as crown and bridge materials either with or without an alloy substrate, as reconstructive materials, restorative materials, filling materials, inlays, onlays, laminate veneers, dental adhesives, cements, sealants and the like.
In recent years, materials used for dental restorations have comprised principally of acrylate or methacrylate resins. Typical acrylic resinous materials are disclosed, for example, in U.S. Pat. No. 3,066,112 to Bowen, U.S. Pat. No. 3,194,784 to Bowen, and U.S. Pat. No. 3,926,906 to Lee et al. An especially important methacrylate monomer is the condensation product of bisphenol A and glycidyl methacrylate, 2,2′-bis [4-(3-methacryloxy-2-hydroxy propoxy)-phenyl]-propane (Bis-GMA). Alternatively, BisGMA may be synthesized from the diglycidyl ether of bisphenol A and methacrylic acid (see U.S. Pat. No. 3,066,112 to Bowen).
Because the wear and abrasion characteristics and the overall physical, mechanical, and optical properties of these unfilled acrylic resinous materials is poor, and because acrylic resin systems exhibit high coefficients of thermal expansion relative to the coefficient of thermal expansion of the tooth structure, these substances by themselves are less than satisfactory. In particular, the disparity in thermal expansion coupled with high shrinkage upon polymerization results in poor marginal adaptability, and ultimately leads to secondary decay. Composite acrylic dental restorative materials containing acrylate or methacrylate resins and fillers were thus developed, the fillers generally comprise inorganic materials based on silica, silicate based glasses, or quartz. These filled compositions are useful for a variety of dental treatments and restorative functions including crown and bridge materials, fillings, adhesives, sealants, luting agents or cements, denture base materials, orthodontic materials and sealants, and other dental restorative materials. Despite their suitability for their intended purposes, however, many of these materials have shrinkages of about two to about 4% by volume upon polymerization.
Alternative resinous materials include the ring-opening polymerization of epoxides. These resins have lower shrinkage than methacrylates, but exhibit compatibility problems with methacrylate bonding adhesives and cements when used together.
Epoxy/(meth)acrylate containing compounds containing both epoxy and (meth)acrylate functionality are also known and are obtained from reaction of multi-epoxide containing compound with one or less equivalent of (meth)acrylic acid, or reaction of hydroxyl containing (meth)acrylate with epichlorohydrin. Commercially available epoxy/methacrylate include 3,4-epoxy-cyclohexyl methyl methacrylate from Daicel Chemical, Japan. U.S. Pat. No. 6,187,833 to Oxman et al. generally discloses photocurable compositions containing an epoxy resin, a hydroxyl-containing material, and optionally a free radically polymerizable material. The compositions contain a ternary photoinitiator system comprising an iodonium salt, a visible light sensitizer, and an electron donor compound. Oxman et al. disclose a bifunctional epoxy/acrylate material, but do not disclose an epoxy/acrylate oligomeric material made from the reaction product of a multi-epoxide containing compound and hydroxy (meth)acrylate.
There remains a need in the art for dental resin materials that have minimal shrinkage without sacrificing other advantageous physical properties. It is further desirable to improve other properties of the cured material such as fracture toughness.